Phase change materials are known in the art for use in phase change memory. One common phase change material is Ge2Sb2Te5, which is deposited by physical vapor deposition (PVD), chemical vapor deposition (CVD) or ALD. One disadvantage of PVD processes is that the process is not useful to deposit Ge2Sb2Te5 in small structures, such as small vias or openings, which are becoming more commonplace as the size of semiconductor devices decreases.
Conventional ALD processes are well-suited for depositing highly conformal layers of GeSbTe materials in small openings or vias. However, compositions of GeSbTe materials that are capable of being deposited by these ALD processes are limited in the ratio of elements that can be present due to the chemistries of Ge, Sb, and Te. The stoichiometry of the GeSbTe material is fixed based on the precursors used. Only GeSbTe materials having compositions that fall on the GeTe or GeTe2 and Sb2Te3 tie-lines for GeSbTe materials are possible by conventional ALD processes. While various precursors for ALD of GeSbTe materials are known, one problem with conventional ALD processes is that the composition of the resulting GeSbTe material is limited by the mechanisms of the ligand exchange reaction. For instance, if Ge(II)Cl2 and Te(II)(TMS)2 are used as precursors, GeTe is the predominant material formed by ALD. If Ge(IV)Cl4 and Te(II)(TMS)2 are used as the precursors, GeTe2 is the predominant material formed by ALD. If Ge(IV)(OEt)4 and Te(II)(TMS)2 are used as the precursors, GeTe2 is the predominant material formed by ALD. If Sb(III)(OEt)3 and Te(II)(TMS)2 are used as the precursors, Sb2Te3 is the predominant material formed by ALD. If Sb(III)Cl3 and Te(II)(TMS)2 are used as the precursors, Sb2Te3 is the predominant material formed by ALD. Other stoichiometries of the metals relative to one another are not possible.
As the size of semiconductor devices continue to decrease, it would be desirable to be able to deposit GeSbTe materials in small vias or openings by ALD. In addition, it would be desirable to have an ALD process that is capable of producing GeSbTe materials of other stoichiometries, such as stoichiometries that are off the composition tie-line.